Co-channel interference limits the number of simultaneous users in today's wireless systems; techniques for efficient co-channel interference rejection in wireless communication systems are of great importance. Recently, antenna arrays have been proposed to obtain extra degrees of freedom, so that spatio-temporal processing may be used for interference rejection. In some cases it is infeasible or unattractive to employ antenna arrays.
The increased number of users in wireless systems motivates the research in the area of interference rejection techniques. In order to suppress interfering co-channel signals some degree of freedom in the received signal is generally exploited. This freedom may be obtained by using multiple receiving antennas at the base station and/or by exploiting temporal structure in the communication signal.
Use of antenna arrays in wireless systems has been intensively investigated recently; see P. Zetterberg and B. Ottersten, “The spectrum efficiency of a basestation antenna array system for spatially selective transmission”, IEEE Transactions on Vehicular Technology, 44(3): 651-660, August 1995, F. Pipon, P. Chevalier, P. Vila and J. -J. Monot, “Joint spatial and temporal equalisation for channels with ISI—theoretical and experimental results for a base station antenna array”, in Conference proceedings of Signal Processing Advances in Wireless Communications (SPAWC), pages 309-312, Paris, April 1997 IEEE, or D. Asztély and B. Ottersten, “MLSE and spatio-temporal interference rejection combining with antenna arrays”, in IX European Signal processing Conference (EUSIPCO-98), island of Rhodes, Greece, Sep. 8-11 1998.
Multi-dimensional antenna array signal processing is traditionally focused on utilising the spatial dimension present in array output data. The temporal dimension (delay-spread) has until recently been dealt with in separate circuits (channel equalisation). Combined temporal and spatial processing, as noted in D. T. M. Slock, “An interference cancelling multichannel matched filter”, in Communications Theosy Mini-Conference in conjunction with Globecom, pages 214-218, New York, N.Y., 1996, IEEE and in A. J. Paulray and C. B. Papadias, “Space-time processing for wireless communications”, IEEE Signal Processing Magazine, 14(6): 49-83, 1997, is advantageous when constructing highly efficient receiver methods for interference rejection. Drawbacks with antenna arrays are the increase in hardware and the difficulty to implement them on mobile stations. The present invention describes a method and a receiver for adaptive co-channel interference rejection using one or more antennas.
The method and the receiver according to the present invention are set forth through the attached independent claims. Further embodiments of the invention are set forth through attached dependent claims.